JPH0685370A - Optical fiber amplifier - Google Patents

Abstract

PURPOSE:To inhibit the amplification of spontaneous emission light, which is generated by an optical amplification fiber, to make it possible to obtain a low noise and a high gain in an optical fiber amplifier. CONSTITUTION:When excitation lights, which are generated by excitation light sources 2 and 4, are introduced into an optical amplification fiber part 1 through multiplexer/branching filter 3 and 5, the excitation lights are by-pass via a multiplexer/branching filter 9, an optical fiber 12 and a multiplexer/branching filter 10 and optical amplification fibers 6 and 7 are excited. When signal light is inputted in the fiber part 1 in this state, the signal light is amplified by an induced emission while being propagated in the interior of the fiber 6 and moreover, the signal light is further amplified and is outputted while being propagated in the interior of the fiber 7 via the filter 9, an optical isolator 11 and the filter 10. Spontaneous emission light generated by the fiber 7 is intercepted by the isolator 11 via the filter 10 and is not propagated to the fiber 6 and an increase in a noise in the fiber 6 is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber amplifier, and more particularly to a bidirectional pumping optical fiber amplifier which introduces pumping light from both the signal light input side and the signal light output side of an optical amplifying fiber.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 2, an optical fiber amplifier of this type has shown in FIG. 2 a pumping light generated by one or a plurality of pumping light sources 22 on the signal light input side of an optical amplifying fiber 21 and a signal of an optical transmission line. A multiplexer / demultiplexer (or multiplexer) that combines with light 2
3 is connected to introduce a pumping light generated by one or a plurality of pumping light sources 24 to the signal light output side of the optical amplification fiber 21 from the signal light output side of the optical amplification fiber 21 (or a multiplexer). 25 was connected.

In such a conventional optical fiber amplifier,
The pumping light source 2 passes through the multiplexer / demultiplexers 23 and 25 located on the signal light input side and the signal light output side of the optical amplification fiber 21.
By introducing the pumping light (having a wavelength band different from that of the signal light) generated by 2 and 24 into the optical amplifying fiber 21, the optical amplifying fiber 21 is brought into an excited state. In this state, when the signal light is input from the signal light input side, the signal light is amplified by stimulated emission while propagating inside the optical amplification fiber 21, and is emitted from the signal light output side.

[0004]

In this conventional optical fiber amplifier, the spontaneous emission light (having the same wavelength band as the signal light) generated by the optical amplification fiber 21 itself is located at the input / output end of the optical amplification fiber 21. Since the light is reflected by the optical component, when the gain of the optical fiber amplifier is increased, the spontaneous emission light is amplified one after another, which causes the deterioration of the noise characteristic and the decrease of the small signal gain.

In view of the above points, an object of the present invention is to construct an optical amplifying fiber section by connecting an optical circuit in series between two or more sets of optical amplifying fibers, and input signal light into the optical signal by the optical circuit. To achieve low noise by passing only the signal light to the signal light output side, and also to obtain high gain by passing the pumping light in both directions between the signal light input side and the signal light output side. To provide the optical fiber amplifier.

[0006]

The optical fiber amplifier of the present invention combines the pumping light and the signal light generated by the pumping light source on the signal light input side of the optical amplification fiber that absorbs the pumping light and amplifies the signal light. Then, a multiplexer for connecting to the optical amplifying fiber is connected, and a multiplexer for introducing pumping light generated by a pumping light source to the signal light output side of the optical amplifying fiber from the signal light output side of the optical amplifying fiber. In the bidirectional pumping optical fiber amplifier to be connected, the optical amplifying fiber section passes in the middle of each of two or more sets of optical amplifying fibers, and the signal light passes from the input port to the output port only in one direction and in the opposite direction. Is characterized in that an optical circuit having such a characteristic that the pumping light that does not pass through is transmitted in both directions from the input port to the output port and from the output port to the input port is connected in series.

[0007]

In the optical fiber amplifier of the present invention, when the pumping light generated by the pumping light source is introduced into the optical amplifying fiber section through the multiplexers located on the signal light input side and the signal light output side of the optical amplifying fiber section, the pumping light is generated. Passes through the optical circuit in both directions of the signal light input side and the signal light output side to excite the optical amplification fiber. In this pumped state, when signal light is input from the signal light input side, the signal light is amplified by stimulated emission while propagating inside the optical amplification fiber on the signal light input side,
Further, it is further amplified by stimulated emission while propagating inside the optical amplification fiber on the signal light output side via the optical circuit. On the other hand, the spontaneous emission light generated by the optical amplification fiber on the signal light input side is propagated through the optical circuit to the optical amplification fiber on the signal light output side and amplified and output together with the signal light. The spontaneous emission light generated by the optical amplification fiber is blocked by the optical circuit and does not propagate to the optical amplification fiber on the signal light input side, and the increase of noise in the optical amplification fiber on the signal light input side is prevented.

[0008]

The present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an optical fiber amplifier according to an embodiment of the present invention. The optical fiber amplifier of the present embodiment combines the pumping light generated by the pumping light source 2 and the signal light of the optical transmission line on the signal light input side of the optical amplifying fiber unit 1 and introduces the multiplexed light into the optical amplifying fiber 6. A pump (or a multiplexer) 3 is connected, and the pumping light generated by the pumping light source 4 is supplied to the optical amplification fiber section 1 on the signal light output side of the optical amplification fiber section 1.
Multiplexer / demultiplexer (or multiplexer) introduced from the signal light output side of
5 is a bidirectional pumping optical fiber amplifier.

The optical amplification fiber section 1 is constructed by connecting an optical circuit 8 in series between two sets of optical amplification fibers 6 and 7 that absorb pumping light and amplify signal light.

In the optical circuit 8, the signal light passes only in one direction from the input port to the output port and does not pass in the opposite direction. The pumping light goes in both directions from the input port to the output port and from the output port to the input port. It is an optical circuit having a characteristic of passing through. In this embodiment, in the optical circuit 8, the multiplexers / demultiplexers 9 and 10 are connected in series to the input / output ends of the optical isolator 11, and the pumping optical ports of the multiplexers / demultiplexers 9 and 10 are connected by the optical fiber 12. Has been realized.

Next, the operation of the optical fiber amplifier of the present embodiment thus constructed will be described.

The pumping light (having a wavelength band different from that of the signal light) generated by the pumping light sources 2 and 4 is supplied to the optical amplifying fiber section 1.
When introduced into the optical amplification fiber section 1 through the multiplexer / demultiplexers 3 and 5 located on the signal light input side and the signal light output side of
The pumping light generated by the pumping light source 2 puts the optical amplification fiber 6 on the signal light input side into a pumping state, and passes through the multiplexer / demultiplexer 9, the optical fiber 12 and the multiplexer / demultiplexer 10 on the signal light output side. The amplifying fiber 7 is also in the excited state. The pumping light generated by the pumping light source 4 puts the optical amplification fiber 7 on the signal light output side into a pumping state, and passes through the multiplexer / demultiplexer 10, the optical fiber 12 and the multiplexer / demultiplexer 9 on the signal light input side. The optical amplification fiber 6 is also set in the excited state.

When the signal light is input from the signal light input side in the pumping state of the optical amplifying fibers 6 and 7, the pumping light and the signal light are multiplexed by the multiplexer / demultiplexer 3, and the optical amplifying fiber 6 While propagating inside, the signal light is amplified by stimulated emission and input to the multiplexer / demultiplexer 9.

Of the input signal light and pump light, the multiplexer / demultiplexer 9 splits the signal light toward the optical isolator 11 and the pump light toward the optical fiber 12.

The signal light branched in the direction of the optical isolator 11 passes through the optical isolator 11 and the multiplexer / demultiplexer 10, is introduced into the optical amplification fiber 7 on the signal light output side, and propagates inside the optical amplification fiber 7. In the meantime, it is further amplified by stimulated emission and output to the signal light output side via the multiplexer / demultiplexer 5.

By the way, since the spontaneous emission light generated by the optical amplification fiber 6 on the signal light input side has the same wavelength band as the signal light, the signal light is transmitted through the multiplexer / demultiplexer 9, the optical isolator 11 and the multiplexer / demultiplexer 10. Although it is propagated to the output side optical amplification fiber 7 and amplified together with the signal light and output, the spontaneous emission light generated by the signal light output side optical amplification fiber 7 is also in the same wavelength band as the signal light, so it is combined. It passes through the wave filter 10 and is blocked by the optical isolator 11, and does not propagate to the optical amplification fiber 6 on the signal light input side.

In the optical fiber amplifier of this embodiment, since the amplification is carried out in two stages, that is, the amplification by the optical amplification fiber 6 on the input side of the signal light and the amplification by the amplification fiber 7 on the output side of the signal light, the total noise is reduced. The fact that the spontaneous emission light generated by the optical amplification fiber 7 on the signal light output side is not propagated to the optical amplification fiber 6 on the signal light input side, which has a large degree of determining the index, plays a major role in reducing the overall noise index. Fulfill

3 and 4 are diagrams for comparing the gain-optical output characteristic and the noise figure-gain characteristic of the optical fiber amplifier of this embodiment and the conventional optical fiber amplifier. The characteristic (b) of the optical fiber amplifier of the present embodiment and the characteristic (a) of the conventional optical fiber amplifier are shown for comparison. The optical fiber amplifier of the present embodiment is configured so that the pumping light is passed in both directions between the signal light input side and the signal light output side when two-stage amplification is performed by the two sets of optical amplification fibers 6 and 7. Since it is used effectively, compared to conventional optical fiber amplifiers,
The gain is high in the non-saturated region of the optical output (see FIG. 3). Further, for example, the intensity of the pumping light generated from the pumping light source 4 is changed after the pumping light generated from the pumping light source 2 is optimally adjusted to minimize the noise figure of the spontaneous emission light generated in the optical amplification fiber 6. If the gain is adjusted to adjust the gain, the noise figure becomes almost constant regardless of the gain (see FIG. 4).

In the above embodiment, the optical amplifying fiber section 1 includes two sets of optical amplifying fibers 6 and 7 and one optical circuit 8.
Although the description has been given by taking as an example the case where the optical amplification fiber section is configured with the above, the present invention can be similarly implemented if the optical amplification fiber section has a configuration in which an optical circuit is connected in series in the middle of each of the two or more sets of optical amplification fibers. Absent.

[0021]

As described above, according to the present invention, in the bidirectional pumping optical fiber amplifier, the optical amplifying fiber section is configured such that an optical circuit is connected in series in the middle of each of two or more sets of optical amplifying fibers. Low noise is realized by not allowing the spontaneous emission light generated in the optical amplification fiber on the signal light output side to propagate to the optical amplification fiber on the signal light input side by passing the signal from the signal light input side only to the signal light output side, and By bypassing the pumping light and passing it in both directions between the signal light input side and the signal light output side, it is possible to effectively use the pumping light and obtain a high gain.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an optical fiber amplifier according to an embodiment of the present invention.

FIG. 2 is a block diagram showing an example of a conventional optical fiber amplifier.

FIG. 3 is a diagram comparing gain-optical output characteristics of the optical fiber amplifier of the present embodiment and a conventional optical fiber amplifier.

FIG. 4 is a diagram comparing the noise figure-gain characteristics of the optical fiber amplifier of the present embodiment and the conventional optical fiber amplifier.

[Explanation of symbols]

 1 Optical amplification fiber part 2,4 Pumping light source 3,5 Multiplexing / demultiplexing device (multiplexing device) 6,7 Optical amplification fiber 8 Optical circuit 9,10 Multiplexing / demultiplexing device 11 Optical isolator 12 Optical fiber

Claims (1)

[Claims] 1. A multiplexer for multiplexing the pumping light and the signal light generated by the pumping light source on the signal light input side of an optical amplification fiber for absorbing the pumping light and amplifying the signal light, and introducing the multiplexed light into the optical amplification fiber. In a bidirectional pumping optical fiber amplifier connecting a multiplexer for introducing pumping light generated by a pumping light source to the signal light output side of the optical amplifying fiber from the signal light output side of the optical amplifying fiber, The amplifying fiber part passes the signal light only in one direction from the input port to the output port and does not pass in the opposite direction in the middle of each of the two or more sets of optical amplifying fibers. The pumping light goes from the input port to the output port. An optical fiber amplifier having a configuration in which optical circuits having a characteristic of passing in both directions from an output port to an input port are connected in series.